The object of the present invention is a hinge for the elastic articulation of a temple piece to the front frame of an eyeglass frame comprising a first hinge element fastened on the front frame and shaped externally in accordance with a cam profile, a second hinge element telescopically guided on the temple piece and urged by a spring into a retracted position within the temple piece, and a lug fastened on the temple piece and acting on the said cam profile.
The known hinges of this type offer the possibility of a preestablished stable positioning of the temple pieces in a folded position (for the putting away of the eyeglasses) or in an open position (for their use), and they furthermore make it possible to move the temple pieces elastically a short distance beyond the open position.
The reliability of these hinges, namely the ability to assure service which is constant in time, constitutes one of the main requirements expressed by the manufacturers of eyeglass frames.
Another fundamental requirement, which in a certain sense is contrary to the previous one, is the necessity of miniaturizing the hinge and its components as much as possible; by way of illustration, it may be stated that the aforementioned lug is generally not longer than 2 to 2.5 mm.
In accordance with the teaching of the prior art it has been customary up to now to fasten the lug to the temple piece by a screw which passes through it. The surface of the lug facing the cam profile has in such case the function of an abutment for the spring of the second hinge element.
This technical solution means that the lug must be made of very resistant material, such as, for instance, hardened steel.
However, if the lug is made of steel it is necessary to use a similar material also for the first hinge element, or at least for the surface thereof constituting the cam profile.
A teaching of this kind is, for instance, given in Italian Patent Application 22325-B/81 of the same applicant.
Among the main drawbacks of this technical solution the following may be pointed out:
the difficulty in working the materials used, which gives rise, among other things, to a high cost of manufacture of the hinge, PA1 the difficulty in mounting the components of the hinge, in particular the lug, PA1 the possibility of the sticking of the hinge due to the rusting of its parts which are made of steel.